I have a 2003 Velocity 260 w/496 Mag (non-ho). I have had whipple do their stage 2 tune with the 120 degree T-stat. Dustin at whipple did mention with this flash I would see a little bit of soot because of the tune required the use of 91+ octane premium fuel. However I think what I am experiencing is way, way too much soot........

Today the air temp was right around 75 and I am guessing the water temp is in the mid 60s. Im currently running 87 octane (as the soot gets worse the higher the octane). I took a run at 3/4 throttle (4300-4500 RPM) for about 10 miles (round trip) with myself and 2 other guys. There was aproximately 1/2 a tank of fuel. Within this 10 miles the transom was completly covered in dark gressy soot. As far as performace, the boat ran 65 MPH (on GPS) at 3/4 throttle, so top end performance is where it should be... When I run the boat at lowere throttle (maybe around 3500-4000 RPM) I see much less soot, but still quite a bit. The soot is very greesy and difficult to clean. I have had the codes read numerous times and nothing out of the ordinary..... I have also put a fuel pressure gauge on it running at idle and at WOT (I don't remember the numbers off hand but they were right in line with what is expected, did this last season). I have been fighting this since I bought the boat and I am to the point where I am willing to yank out the 496 and drop in something else. ..... THe 496 has been super reliable but this soot make my boat look like a POS within minutes of running......

Any suggestions of what to do next? I figure if it was a bad vavle or valve seat, I would see greate amounts of soot on the side where the bad valve would be right? The soot is pretty much evenly distributed..... THe boat doesn't smell rich (at least from the cockpit).

ANy help or suggestions would be greatly appreciated.

While this pic was taken last season, this is about what I saw after my 10 minute run. I ran it much harder on Sunday and the soot was MUCH worse than this photo. the transom was almost entirely black...... Also the exhaust tips have been replaced with longer ones with internal flappers, as I was hoping this would get the exhaust soot out beyond the platform....... Have run without the platform and still the transom covered in soot....

Put a 160 degree thermostat back in the engine and then tell us how much better the soot issue is.

Best Regards,
Ray @ Raylar

Did the stock engine run any faster or better in the boat after the stage 2?

The stat won't matter as the colder one only opens sooner and stays open all the time. The engine still runs same temps.

huh? I don't think so. They don't just open up all the way and stay there.

At WOT my 496 is running right around 120 degrees at the exhaust manifolds (raw water) with a nice 165 degree engine temp due to the correct thermostat.

Yikes! My 496HO is an 11/2002 version with the original flash on the PCM. Ran for 4 hours straight last weekend with 89-octane. No soot at all! WTF?! That is bad dude!

Last year, before I received the 120 T-Stat, I did run the boat with the stock T-Stat. Result was the same. Using the 120 t-stat the boat runs all day at 160. With stock t-stat it ran about 170ish.

Is the boat faster after the flash? Yes! How much faster? About 1-2 MPH, but the major difference is in low end grunt. It pops up on plan effortlessly.... Once on plane, running at 3000 ish, if you nail the throttle it will knock you over if you not holding on to something. The torque is where the flash made the major difference.

One thing to note, as water temps increase, the soot does decrease a bit when mildly usin the motor. But if making 3/4 - full throttle blasts, the heavy soot remains about the same regardless of air/water temps.....

Also the soot was worse before the whipped stage 2 flash.

these guys know a lot more than I do, but Mark at Precision did both my 496HO upgrades. dyno'd one before headers and after header install to tune both computers...no soot issues what so ever, 45hp gain per motor. I run 92 only now tho. I did not have a soot issue before either

Ok, well you may "think" so but I've actually done the testing and fought my way through more issues with this engine than probably most other 496 owners. I don't know it all but before you simply go by a text book answer, consider this:

1. You just compared the raw water temp with the coolant temp - two completely different things in a closed-cooled boat engine. Of course the exhaust temp is about 120 as it is in just about everything stock. The stat has NOTHING to do with raw water temps. It only has to do with "when" the antifreeze is moved around inside the system to the heat exchanger. Take a look at where it is..

2. With a stock stat or Dustin's 120, the only difference is the very slight speed at which they warm up. The 496 runs 160+ at idle and a little cooler at faster speeds but NEVER at 120 degrees. So yes, both stats will net the same coolant temp when running and I know because I've seen it in mine. And it was one of the things we noticed right away after installation.

When we had a stock engine, it ran 160 at slower speeds and slightly cooler once you start getting into it.

When I did the 525 upgrade and made more heat with that package the temps stayed the same with more heat but same stat.

When I did the 600 (the first time), we bought the 120 stat and the warm-up time barely changed but all the operating temps stayed the same and this package makes even more B.T.U.'s.

The only fluid that had any significant differences in temp was the engine oil itself as power was upgraded each time.

Yes, they do open up and pretty much stay there. There is no diff in that engine from 120 to 160 because the engine runs 160+ anyway.. When it cools down on plane, it's still well above 150.

The other thing to consider is that most guys read off the gauge at the helm. I still say very few boat gauges out there read well with accuracy with much consistency.

I find that the 3 wire senders "seem" to be more accurate and consistently give slightly better readings on that engine.

Is your motor using any oil? I had what I thought was a soot problem last year but it was actually oil. Just a thought.